In the past, a substrate treatment method which uses liquid enchant which contains phosphoric acid (H3PO4) to etch a silicon semiconductor wafer (substrate) on which a nitride film (Si3N4) and oxide film (SiO2) are formed has been proposed (see PLT 1). In this substrate treatment method, a plurality of semiconductor wafers are dipped into the liquid enchant which contains phosphoric acid (H3PO4) which is stored in an etching tank so that the plurality of semiconductor wafers sire etched all together. In this etching treatment, the phosphoric acid in the liquid etchant acts as a catalyst whereby the semiconductor wafers are stripped of their nitride films (Si3N4).
Further, the used liquid etchant which remains inside the etching treatment tank after the etching treatment is transferred through a receiving tank to a treatment tank of a regenerating system. Inside the treatment tank in which the used liquid etchant is stored, a suitable quantity of liquid hydrofluoric acid (HF) for the amount of the used liquid etchant is added. In the treatment tank, under a relatively high temperature predetermined temperature environment, the used liquid etchant which contains ingredients based on the nitrides which are removed by the etching treatment and liquid hydrofluoric acid (HF) are mixed and reacted whereby the phosphoric acid (H3PO4) is regenerated. This regenerated phosphoric acid (H3PO4) is returned to the liquid etchant to be used for the etching treatment.
According to such a substrate treatment method, since the phosphoric acid is regenerated from the used liquid etchant which remains after the etching treatment and that phosphoric acid is returned to the liquid etchant to be used for the etching treatment, it is possible to make effective use of the phosphoric acid while continuing to perform etching treatment on the semiconductor wafers for removing the nitride films.